High numbers in the US among sufferers of meat allergy
More than 110,000 people in the US have been diagnosed with “meat allergies” to red meat in the past 13 years. The US health authority CDC reported this at the end of July after evaluating the results of the Eurofins Viracor test laboratory from 2010 to 2012, which was the main laboratory for this evidence until 2021. In many cases, a bite from the lone star tick (Amblyomma americanum) has caused a potentially life-threatening allergy to a sugar molecule found primarily in red meat: galactose-1,3-alpha-galactose (alpha- Gal). According to the CDC, the allergy occurred most frequently in those US states in which there are established Lone Star tick populations. Between 2017 and 2021, the number of positive meat allergy tests increased by 15,000 each year.
Ticks trigger meat allergies
The fact that ticks can trigger a meat allergy is not new in itself. What is surprising, however, is how many people are now affected in the USA: Because the CDC assumes a huge number of unreported cases, the actual number of meat allergy sufferers in the USA could be up to 450,000. According to a second CDC investigation, an important reason for the massive underreporting could be that the required tests are not carried out enough because many doctors and nurses are hardly familiar with this trigger route.
The CDC survey of 1,500 healthcare workers found that 50 percent of general practitioners, internists, pediatricians, and nurses had never heard of Alpha Gal Syndrome (AGS), as the meat allergy is officially called. And if they did, a third of those surveyed were still “not too sure” about being able to adequately diagnose and care for the allergy. Only five percent felt “very safe”.
Alpha-Gal is a sugar and is mainly found in red meat, i.e. in beef, pork, lamb, rabbit and game meat as well as in the offal of these animals. The problematic sugar is also found in other animal products, such as milk, dairy products such as cream and cheese, and gelatine, albeit often in smaller amounts. Poultry and fish, on the other hand, can be consumed safely by those affected. Drugs coated with gelatin can also cause mild to severe allergic reactions.
Clinical picture also in Germany
However, because the symptoms are diverse and non-specific and often only appear up to seven hours after eating meat or dairy products, it is not easy for those affected and doctors to suspect correctly. “There are still no epidemiological figures for AGS for Germany or Europe,” says allergist Tilo Biedermann from the Technical University of Munich. “But wherever there are ticks, there is also this clinical picture. In our case, it does not depend on a specific species of tick, but many are able to transmit AGS, including the common wood tick.”
Tick bites are the most common trigger
An allergy to red meat can develop in a number of ways. Tick bites are one of the most common triggers. The parasites also transfer with their saliva the sugar compound that they have produced themselves or that come from previous blood meals from other alpha-gal-producing animals such as deer. Then Alpha-Gal can trigger an allergy through the skin – not the bloodstream – even if one has not previously had a problem with red meat or other foods.
This does not always result in a fully developed allergy. Often one only becomes sensitized and continues to tolerate the antigen in certain amounts. However, repeated tick bites can exacerbate this allergy, or eating a very large amount of red meat such as a large steak – and co-factors such as exercise – can still trigger an allergy. “We normally have a high immune tolerance for food,” explains Biedermann. “But it probably doesn’t reach deep enough into the skin, or at a strength, to be effective against a tick bite.”
Hunters and forest workers affected relatively often
The skin is a large, highly competent immune organ. However, since the ticks remain in the skin for a very long time with the help of their mouthparts and a kind of biological cement, repeatedly sucking and spitting into the wound, “it can lead to sensitization or even an allergy, especially if there are several tick bites per year,” says Biedermann.
He is therefore not surprised that hunters and forest workers are relatively often sensitized to alpha-gal. Hunters in particular are crawled and stung by up to 200 tick nymphs, the stage between larvae and adult animals, when eviscerating wild animals, and “can sometimes react systemically”.
If a meat allergy is suspected, Biedermann carries out both a skin and a blood test. If both tests are positive, sensitization is certain and an allergy is possible. The question of a therapy arises: Oral desensitization, i.e. via food, is possible under certain circumstances, but not trivial. Biedermann’s team is currently planning a study on this.
“One would like to increase the oral immune tolerance, so to speak, to compensate for the sensitivity. But there is always a risk of triggering an allergic reaction,” says the allergist. “However, if patients only react to a certain amount in the provocation test via food or even only with cofactors such as exertion, then we no longer advise completely avoiding red meat.” Consumption in the non-critical range is then still possible and maybe even increases tolerance.
Evolutionary cause of the allergy
According to researchers, the fact that we humans can become allergic to the sugar alpha-gal could be due to a “catastrophic epidemiological event” 20 to 28 million years ago, which “combined with the almost complete extinction of hominoids. )” as stated in the publication “British Society Immunology”. The ancestors of the African and Asian monkeys (Old World monkeys) and the great apes, including the genus Homo, lost the ability to produce alpha-gal themselves.
From then on, antibodies against Alpha-Gal (from the IgG and IgM class, but not the IgE antibodies formed in allergies) circulated in their blood, which – true to the motto “luck in misfortune” – at the same time led to an evolutionary advantage: these antibodies helped fight off alpha-gal-producing pathogens such as viruses, bacteria, and human-pathogenic protozoa.
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